.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Modified Sat Jul 24 21:42:42 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Tue Oct 22 23:44:11 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified Thu Jun  2 23:44:11 2016 by Nikos Mavrogiannopoulos <nmav@redhat.com>
.TH ASSERT 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
assert \- abort the program if assertion is false
.SH SYNOPSIS
.nf
.B #include <assert.h>
.PP
.BI "void assert(scalar " expression );
.fi
.SH DESCRIPTION
This macro can help programmers find bugs in their programs,
or handle exceptional cases
via a crash that will produce limited debugging output.
.PP
If
.I expression
is false (i.e., compares equal to zero),
.BR assert ()
prints an error message to standard error
and terminates the program by calling
.BR abort (3).
The error message includes the name of the file and function containing the
.BR assert ()
call, the source code line number of the call, and the text of the argument;
something like:
.PP
.in +4n
.EX
prog: some_file.c:16: some_func: Assertion \`val == 0\(aq failed.
.EE
.in
.PP
If the macro
.B NDEBUG
is defined at the moment
.I <assert.h>
was last included, the macro
.BR assert ()
generates no code, and hence does nothing at all.
It is not recommended to define
.B NDEBUG
if using
.BR assert ()
to detect error conditions since the software
may behave non-deterministically.
.SH RETURN VALUE
No value is returned.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR assert ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99.
In C89,
.I expression
is required to be of type
.I int
and undefined behavior results if it is not, but in C99
it may have any scalar type.
.\" See Defect Report 107 for more details.
.SH BUGS
.BR assert ()
is implemented as a macro; if the expression tested has side-effects,
program behavior will be different depending on whether
.B NDEBUG
is defined.
This may create Heisenbugs which go away when debugging
is turned on.
.SH SEE ALSO
.BR abort (3),
.BR assert_perror (3),
.BR exit (3)
.SH COLOPHON
This page is part of release 5.13 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
